(a) Field of the Invention
The present invention relates to a liquid crystal display (LCD) device having a uniform cell gap, and more particularly, to an improvement in the structure of pillar spacers being disposed in the liquid crystal of the LCD device.
(b) Description of the Related Art
LCD devices have been increasingly used in a variety of applications. The LCD device has a pair of opposing panels which define therebetween a cell gap for receiving therein liquid crystal. A pair of electrodes are disposed sandwiching therebetween the liquid crystal to apply a voltage across the liquid crystal, whereby orientations of the liquid crystal (LC) molecules are controlled to display an image on the front panel of the LCD device. A large number of spacers such as ball spacers or pillar spacers are disposed between both the panels to maintain a uniform cell gap irrespective of an external force being applied between the panels.
FIG. 9 shows a conventional LCD device, which includes a color filter panel including a color filter substrate 11, a TFT panel including a TFT substrate 12, and LC layer 13 encapsulated within the cell gap 13 formed between the color filter panel and the TFT panel 12. A plurality of pixels are defined on the TFT panel by electrode lines extending in the column and row directions. Each pixel includes a pixel electrode, a common electrode and a thin film transistor (TFT) for driving the pixel electrode.
A black matrix film 15, a color film 16, and an overcoat film 17 are consecutively formed on the color filter substrate 11. A gate electrode line 25 disposed for a row of TFTs is shown on the TFT substrate 12. In the region for the black matrix film 15 of the color filter substrate 11, i.e., other than the region of the effective pixel area, a pillar spacer 20A extends from the overcoat film 17 toward the TFT panel to abut the gate electrode 25 formed on the TFT substrate 12.
FIG. 10 shows another conventional LCD device, which is similar to the conventional LCD device of FIG. 9, except for the configuration of the pillar spacer 20A which extends from the gate electrode 25 toward the color filter panel to abut the overcoat film 17 on the color filter substrate 11 in the another conventional LCD device.
In both the conventional LCD devices of FIGS. 9 and 10, the cell gap 13 is maintained at a specified distance due to the balance between the compressive stress of the elastic pillar spacers 20A and the compressive load applied between the color filter substrate 11 and the TFT substrate 12.
There is a common problem in both the conventional LCD devices that a relatively small height of the pillar spacers 20A limited by the narrow cell gap 13 has an insufficient elastic force even though an elastic resin material is used for the pillar spacers 20A. In such a case, the pillar spacers 20A may have a larger strain for a minor deformation thereof, and may be subjected to a plastic deformation out of the elastic deformation range if the strain exceeds a specified deformation rate.
In addition, it is difficult for the pillar spacers 20A to expand and contract while following the changing distance of the cell gap 13, which changes due to the expansion and contraction of the liquid crystal 14 caused by a temperature change of the LCD device. More specifically, a higher ambient temperature of the LCD device expands the liquid crystal 14 and increases the distance of the cell gap 13 with an insufficient expansion of some pillar spacers 20A, thereby causing distortion of the display screen. On the other hand, a lower ambient temperature of the LCD device contracts the liquid crystal 14 while less contracting the pillar spacers 20A, thereby causing vacuum state of the LC layer 14 causing vacuum bubbles.
Further, an external force applied between both the substrates 11 and 12 may sometimes cause a plastic deformation of the black matrix film 15, color film 16 or overcoat film 17 due to the abutment of the pillar spacers 20A, thereby causing a local color change of the LCD device.